Description

The anisotropy of wood creates a complex problem for solving heat and mass transfer problems that require analyses be based on fundamental material properties of the wood structure. Most heat transfer models use average thermal properties across either the radial or tangential directions and have not differentiated the effects of cellular alignment, earlywood/latewood differentiation, ring orientation, and moisture content. Two 2-Dimensional finite element models have been developed that take these parameters into consideration. The first model is used to determine the effective thermal conductivities of softwood cellular structure as a function of cell alignment, cell porosity or density, and moisture content. The second model uses the results from the first model to help explain the transient heat transfer effects of ring orientation for any board "cut" from any location in a log, earlywood/latewood ratio, earlywood and latewood densities, and growth rate. This paper, briefly discusses the two models and their development. Initial results are presented showing the effects of density and moisture content on the effective thermal conductivity values for softwood cell structure. Comparisons are made with empirical equations for thermal conductivity of wood in the literature. The second finte element board model is introduced to show the effects of ring orientation at 0% moisture content for several boards "cut" from several locations in a log. These new models are useful for enhancing our understanding of fundamental heat transfer effects in various wood boards.

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This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.